POS1383 DIFFERENTIAL DIAGNOSTICS OF POLYMYALGIA RHEUMATICA IN A UNIVERSITY HOSPITAL IN FINLAND
Authors: J. Paltta, S. Suuronen, L. Pirilä, A. Palomäki
Journal: Annals of the Rheumatic Diseases (2022)

Background Polymyalgia rheumatica (PMR) is an inflammatory disease that causes muscle pain and morning stiffness, especially in the shoulders and hips. Diagnosing PMR can be difficult, as the diagnosis is mainly clinical without a definitive diagnostic test, and many symptoms and findings of PMR may also be present in other conditions. There is little recent data on differential diagnostics of PMR. Objectives The aim of our study was to analyse patients diagnosed with polymyalgia rheumatica (PMR) in Turku University Hospital in Finland and determine how often a competing diagnosis better explaining the patients’ symptoms was found during further evaluation and clinical follow-up. We also aimed to find out what are the most common conditions initially misdiagnosed as PMR. Methods All patients with a new primary diagnosis of PMR (International Classification of Diseases – 10 th revision [ICD-10] code M35.3) on at least one (in- or outpatient) visit during years 2016–2019 were identified from the hospital discharge register of Turku University hospital in Finland. We did a chart review of the patient charts including the full clinical follow-up period (median 34 months). We studied how often the primary diagnosis of PMR changed after further diagnostic evaluation or during follow-up. Results In 125 (32.7%) of the 382 patients, the initial diagnosis of PMR changed during further diagnostic evaluation or follow-up. Most common diagnoses initially misdiagnosed as PMR were inflammatory arthritides 36.0% (45/125), degenerative or stress-related musculoskeletal disorder 12.8% (16/125), infection 9.6% (12/125), malignancy 9.6% (12/125), giant cell vasculitis 6.4% (8/125) and other vasculitis 6.4% (8/125) (Table 1). Diagnosis changed in 19% (39/207) of patients fulfilling the 2012 ACR/EULAR PMR classification criteria and in 49% (86/175) of patients who did not. Table 1. Demographic and clinical characteristics of the study sample. Number of patients 382 Female (%) 218 (57.1%) Age at diagnosis in years [IQR] 70.0 [64.0–77.8] Follow-up in months [IQR] 34.0 [21.0–49.0] Diagnosed in rheumatology (%) 299 (79%) Treated in rheumatology (%) 310 (81%) Nr. of visits [IQR] 6.5 [3.0–12.0] Diagnosis changed during follow-up (%) 125 (32.7%) Final diagnosis in 125 patients whose initial diagnosis of PMR changed Inflammatory arthritides (%) 45 (36.0%) Degenerative or stress-related musculoskeletal disorder (%) 16 (12.8%) Infection (%) 12 (9.6%) Malignancy (%) 12 (9.6%) Giant cell vasculitis (%) 8 (6.4%) Other vasculitis (%) 8 (6.4%) Other rheumatological disease (%) 7 (5.6%) Fibromyalgia or other chronic pain syndrome (%) 4 (3.2%) Gout or other crystal arthropathy (%) 2 (1.6%) Endocrinological disease (%) 2 (1.6%) Other or unknown (%) 14 (11.2%) Continuous variables are expressed as medians with interquartile ranges, and categorical variables are described as counts with percentages. Conclusion In a university hospital setting, a third of initial diagnoses of PMR were changed during further evaluation and follow-up. Our findings highlight that thorough consideration of differential diagnosis is always essential when diagnosing PMR. Especially in patients with atypical presentation, there is a substantial risk for misdiagnosis. Disclosure of Interests Johanna Paltta: None declared, Saara Suuronen: None declared, Laura Pirilä Consultant of: Has received consulting fees from Novartis, UCB, Pfizer, Lilly, Roche, Sanofi, Abbvie, Bristol-Myers-Squibb, Jansen-Cilag, Celgene and MSD, all unrelated to this work, Antti Palomäki Speakers bureau: Has received a lecture fee from Pfizer and Sanofi, all unrelated to this work, Consultant of: Has received consulting fees from Pfizer, Amgen and Abbvie, all unrelated to this work